U.S. patent number 4,320,528 [Application Number 06/114,616] was granted by the patent office on 1982-03-16 for ultrasonic cleaner.
This patent grant is currently assigned to Anco Engineers, Inc.. Invention is credited to Terry D. Scharton, G. Bruce Taylor.
United States Patent |
4,320,528 |
Scharton , et al. |
March 16, 1982 |
Ultrasonic cleaner
Abstract
The present invention relates to methods and apparatus for
cleaning and removing the buildup of products of corrosion,
oxidation, sedimentation and comparable chemical reactions from
various portions of heat exchanger systems such as the location
wherein the primary heat exchanger tubes come in contact with
support plates for those tubes, and the base of said heat
exchanger. The corrosive scale, oxides and other materials can
cause denting of the primary heat exchanger tubes due to the
compressive force of the oxides, scale, and other materials, and
therefore adversely affects the heat exchanging ability of the heat
exchanger system.
Inventors: |
Scharton; Terry D. (Santa
Monica, CA), Taylor; G. Bruce (Culver City, CA) |
Assignee: |
Anco Engineers, Inc. (Culver
City, CA)
|
Family
ID: |
22356356 |
Appl.
No.: |
06/114,616 |
Filed: |
January 23, 1980 |
Current U.S.
Class: |
376/310;
134/1 |
Current CPC
Class: |
F22B
37/483 (20130101); F28G 9/00 (20130101); F28G
7/00 (20130101) |
Current International
Class: |
F22B
37/48 (20060101); F22B 37/00 (20060101); F28G
9/00 (20060101); F28G 7/00 (20060101); G21C
019/32 () |
Field of
Search: |
;176/37 ;165/95,84
;122/380 ;134/1-3 ;376/310 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Chemical Cleaning of BWR and Steam Water System at Dresden Nuc.
Pow. Station, Obrecht et al., pp. 1-18, (10/26/60) 21st Ann. Conf.
of Eng. .
Special Tech. Pub. 42 (1962) ASTM Role of Cavitation in Sonic
Energy Cleaning, Bulat..
|
Primary Examiner: Cangialosi; Sal
Attorney, Agent or Firm: Rozsa; Thomas I.
Claims
We claim:
1. In the art of maintaining a steam generator for a nuclear power
plant in which the steam generator is characterized by an enclosed
tank containing a plurality of heat exchanger tubes and a plurality
of support plates arranged transverse to and sequentially spaced
along the longitudinal axis of the tubes and forming junctions
therewith, where crevices exist between the heat exchanger tubes
and the support plates at the site of the junctions, the junctions
being thereby arranged in a series of groups, and also containing
an outer shell and a metal wrapper inside the tank which envelops
the plurality of tubes and support plates, and wherein magnetite
tends to build up within the crevices at the junctions over a
period of time, the process of removing the magnetite from the
crevices and the junctions while the heat exchanger tubes and
support plates remain in their operative position inside the steam
generator, comprising the steps of:
a. selecting a chemical solvent which when heated to a temperature
between 120 degrees Fahrenheit and 220 degrees Fahrenheit dissolves
magnetite exposed to fresh chemicals at a rate equal to or greater
than about 1.0 inch per 24 hours;
b. adding a metal corrosion inhibitor to said chemical solvent;
c. at least partially filling the tank with said chemical solvent,
so as to establish an initial level which is only a few inches
above the level of the uppermost group of junctions and their
uppermost group of crevices;
d. selecting a plurality of sonic transducers wherein each sonic
transducer has a power output greater than about 0.2 watts per
square centimeter at room temperature;
e. placing said plurality of sonic transducers at a level which is
below the surface of said chemical solvent, substantially in the
plane of said uppermost group of junctions and uppermost group of
crevices and in spaced locations around the circumference of and in
contact with said metal wrapper;
f. running a hot fluid through said heat exchanger tubes so that
the chemical solvent in the region adjacent said junctions and
crevices reaches a temperature between 120 degrees Fahrenheit and
220 degrees Fahrenheit;
g. activating said sonic transducers to a frequency in the range of
about 2 KHZ to 200 KHZ so that sonic energy is transmitted through
said chemical solvent to said junctions and into and laterally of
said crevices whereby cavitation induced at said junctions and at
said crevices by said sonic energy cooperates with said chemical
solvent so as to enhance and accelerate the removal of the
magnetite from said junctions and crevices;
h. continuing the cooperative action of said hot chemical solvent
and said transducers upon said uppermost group of junctions and
crevices until the magnetite is removed from the junctions and
crevices;
i. maintaining said chemical solvent at a temperature between 120
degrees Fahrenheit and 220 degrees Fahrenheit;
j. then lowering the level of said chemical solvent to a height
which is only a few inches above the next group of junctions and
crevices from which magnetite is to be removed, lowering said
plurality of transducers to a corresponding lower location on said
metal wrapper in a plane substantially in alignment with said next
group of junctions and crevices, and again applying said
cooperative effort between said hot chemical solvent and said
transducers until the magnetite is removed from said next group of
junctions and next group of crevices; and
k. continuing in this fashion at the level of each successive group
of junctions and crevices until all of said junctions and crevices
have been cleaned.
2. In the art of maintaining a steam generator for a nuclear power
plane in which the steam generator is characterized by an enclosed
tank containing a plurality of heat exchanger tubes and a plurality
of support plates arranged transverse to and sequentially spaced
along the longitudinal axes of the tubes and forming junctions
therewith, where crevices exist between the heat exchanger tubes
and the support plates at the site of the junctions, the junctions
being thereby arranged in a series of groups, and also containing
an outer shell and a metal wrapper inside the tank which envelops
the plurality of tubes and support plates, and wherein magnetite
tends to build up within the crevices at the junctions over a
period of time, the process of removing the magnetite from the
crevices and the junctions while the heat exchanger tubes and
support plates remain in their operative positions inside the steam
generator, comprising the steps of:
a. selecting a chemical solvent which when heated to a temperature
between 120 degrees Fahrenheit and 220 degrees Fahrenheit dissolves
magnetite exposed to fresh chemicals at a rate equal to or greater
than about 1.0 inch per 24 hours;
b. adding a metal corrosion inhibitor to said chemical solvent;
c. at least partially filling the tank with said chemical solvent,
so as to establish an initial level which is only a few inches
above the level of the lowermost group of junctions and their
lowermost group of crevices;
d. selecting a plurality of sonic transducers wherein each sonic
transducer has a power output greater than about 0.2 watts per
square centimeter at room temperature;
e. placing said plurality of sonic transducers at a level which is
below the surface of said chemical solvent, substantially in the
plane of said lowermost group of junctions and lowermost group of
crevices and in spaced locations around the circumference of and in
contact with said metal wrapper;
f. running a hot fluid through said heat exchanger tubes so that
the chemical solvent in the region adjacent said junctions and
crevices reaches a temperature between 120 degrees Fahrenheit and
220 degrees Farenheit;
g. activating said sonic transducers to a frequency in the range of
about 2 KHZ to 200 KHZ so that sonic energy is transmitted through
said chemical solvent to said junctions and into and laterally of
said crevices whereby cavitation induced at said junctions and at
said crevices by said sonic energy cooperates with said chemical
solvent so as to enhance and accelerate the removal of the
magnetite from said junctions and crevices;
h. continuing the cooperative action of said hot chemical solvent
and said transducers upon said lowermost group of junctions and
crevices until the magnetite is removed from the junctions and
crevices;
i. maintaining said chemical solvent at a temperature between 120
degrees Fahrenheit and 220 degrees Fahrenheit;
j. then raising the level of said chemical solvent to a height
which is only a few inches above the next group of junctions and
crevices from which magnetite is to be removed, raising said
plurality of transducers to a corresponding higher location on said
metal wrapper in a plane substantially in alignment with said next
group of junctions and crevices, and again applying said
cooperative effort between said hot chemical solvent and said
transducers until the magnetite is removed from said next group of
junctions and next group of crevices; and
k. continuing in this fashion at the level of each successive group
of junctions and crevices until all of said junctions and crevices
have been cleaned.
3. In the art of maintaining a steam generator for a nuclear power
plant in which the steam generator is characterized by an enclosed
tank containing a plurality of heat exchanger tubes and a plurality
of support plates arranged transverse to and sequentially spaced
along the longitudinal axes of the tubes and forming junctions
therewith, where crevices exist between the heat exchanger tubes
and the support plates at the site of the junctions, the junctions
being thereby arranged in a series of groups, and also containing
an outer shell and a metal wrapper inside the tank which envelops
the plurality of tubes and support plates, and wherein magnetite
tends to build up within the crevices at the junctions over a
period of time, the process of removing the magnetite from the
crevices and the junctions while the heat exchanger tubes and
support plates remain in their operative positions inside the steam
generator, comprising the steps of:
a. selecting a chemical solvent which when heated to a temperature
between 120 degrees Fahrenheit and 220 degrees Fahrenheit dissolves
magnetite exposed to fresh chemicals at a rate equal to or greater
than about 1.0 inch per 24 hours;
b. adding a metal corrosion inhibitor to said chemical solvent;
c. at least partially filling the tank with said chemical solvent,
so as to establish an initial level which is only a few inches
above the level of the uppermost group of junctions and their
uppermost group of crevices;
d. selecting a plurality of sonic transducers wherein each sonic
transducer has a power output greater than about 0.2 watts per
square centimeter at room temperature;
e. placing said plurality of sonic transducers at a level which is
substantially in the plane of each of said groups of junctions and
in spaced locations around the circumference of and in contact with
said metal wrapper;
f. running a hot fluid through said heat exchanger tubes so that
the chemical solvent in the region adjacent said junctions and
crevices reaches a temperature between 120 degrees Fahrenheit and
220 degrees Fahrenheit;
g. activating all the transducers simultaneously at each level
substantially in the plane of each group of junctions and each
group of crevices to a frequency in the range of about 2 KHZ to 200
KHZ so that sonic energy is transmitted through said chemical
solvent to each group of junctions and into and laterally of each
group of crevices whereby cavitation induced at each group of
junctions and each group of crevices cooperates with said chemical
solvent so as to enhance and accelerate the removal of the
magnetite from the all of the junctions and crevices;
h. continuing the cooperative action of said hot chemical solvent
and said transducers upon each group of junctions and crevices
until the magnetite is removed from all of the junctions and all of
the crevices.
4. In the art of maintaining a steam generator for a nuclear power
plant in which the steam generator is characterized by an enclosed
tank containing a plurality of heat exchanger tubes and a plurality
of support plates arranged transverse to and sequentially spaced
along the longitudinal axes of the tubes and forming junctions
therewith, where crevices exist between the heat exchanger tubes
and the support plates at the site of the junctions, the junctions
being thereby arranged in a series of groups, and also containing
an outer shell and a metal wrapper inside the tank which envelops
the plurality of tubes and support plates, and wherein magnetite
tends to build up within the crevices at the junctions over a
period of time, the process of removing the magnetite from the
crevices and the junctions while the heat exchanger tubes and
support plates remain in their operative positions inside the steam
generator, comprising the steps of:
a. selecting a chemical solvent which when heated to a temperature
between 120 degrees Fahrenheit and 220 degrees Fahrenheit dissolves
magnetite exposed to fresh chemicals at a rate equal to or greater
than about 1.0 inch per 24 hours;
b. adding a metal corrosion inhibitor to said chemical solvent;
c. selecting a plurality of sonic transducers wherein each sonic
transducer has a power output greater than about 0.2 watts per
square centimeter at room temperature;
d. placing said plurality of sonic transducers at a level
substantially in the plane of the uppermost group of junctions and
uppermost group of crevices and in spaced locations around the
circumference of and in contact with said metal wrapper;
e. heating said chemical solvent to a temperature between 120
degrees Fahrenheit and 220 degrees Fahrenheit at a location outside
of said steam generator;
f. at least partially filling the tank with said heated chemical
solvent, so as to establish an initial level which is only a few
inches above the level of the uppermost group of junctions and
their uppermost group of crevices;
g. activating said sonic transducers to a frequency in the range of
about 2 KHZ to 200 KHZ so that sonic energy is transmitted through
said chemical solvent to said junctions and into and laterally of
said crevices whereby cavitation induced at said junctions and at
said crevices by said sonic energy cooperates with said chemical
solvent so as to enhance and accelerate the removal of magnetite
from said junctions and crevices;
h. continuing the cooperative action of said hot chemical solvent
and said transducers upon said uppermost group of junctions and
crevices until the magnetite is removed from the junctions and
crevices;
i. maintaining said chemical solvent at a temperature between 120
degrees Fahrenheit and 220 degrees Fahrenheit;
j. then lowering the level of said chemical solvent to a height
which is only a few inches above the next group of junctions and
crevices from which magnetite is to be removed, lowering said
plurality of transducers to a corresponding lower location on said
metal wrapper in a plane substantially in alignment with said next
group of junctions and crevices, and again applying said
cooperative effort between said hot chemical solvent and said
transducers until the magnetite is removed from said next group of
junctions and next group of crevices; and
k. continuing in this fashion at the level of each successive group
of junctions and crevices until all of said junctions and crevices
have been cleaned.
5. In the art of maintaining a steam generator for a nuclear power
plant in which the steam generator is characterized by an enclosed
tank containing a plurality of heat exchanger tubes and a plurality
of support plates arranged transverse to and sequentially spaced
along the longitudinal axes of the tubes and forming junctions
therewith, where crevices exist between the heat exchanger tubes
and the support plates at the site of the junctions, the junctions
being thereby arranged in a series of groups, and also containing
an outer shell and a metal wrapper inside the tank which envelops
the plurality of tubes and support plates, and wherein magnetite
tends to build up within the crevices at the junctions over a
period of time, the process of removing the magnetite from the
crevices and the junctions while the heat exchanger tubes and
support plates remain in their operative positions inside the steam
generator, comprising the steps of:
a. selecting a chemical solvent which when heated to a temperature
between 120 degrees Fahrenheit and 220 degrees Fahrenheit dissolves
magnetite exposed to fresh chemicals at a rate equal to or greater
than about 1.0 inch per 24 hours;
b. adding a metal corrosion inhibitor to said chemical solvent;
c. selecting a plurality of sonic transducers wherein each sonic
transducer has a power output greater than about 0.2 watts per
square centimeter at room temperature;
d. placing said plurality of sonic transducers at a level
substantially in the plane of the lowermost group of junctions and
lowermost group of crevices and in spaced locations around the
circumference of and in contact with said metal wrapper;
e. heating said chemical solvent to a temperature between 120
degrees Fahrenheit and 220 degrees Fahrenheit at a location outside
of said steam generator;
f. at least partially filling the tank with said heated chemical
solvent, so as to establish an initial level which is only a few
inches above the level of the lowermost group of junctions and
their lowermost group of crevices;
g. activating said sonic transducers to a frequency in the range of
about 2 KHZ to 200 KHZ so that sonic energy is transmitted through
said chemical solvent to said junctions and into and laterally of
said crevices whereby cavitation induced at said junctions and at
said crevices by said sonic energy cooperates with said chemical
solvent so as to enhance and accelerate the removal of the
magnetite from said junctions and crevices;
h. continuing the cooperative action of said hot chemical solvent
and said transducers upon said lowermost group of junctions and
crevices until the magnetite is removed from the junctions and
crevices;
i. maintaining said chemical solvent at a temperature between 120
degrees Fahrenheit and 220 degrees Fahrenheit;
j. then raising the level of said chemical solvent to a height
which is only a few inches above the next group of junctions and
crevices from which magnetite is to be removed, raising said
plurality of transducers to a corresponding higher location on said
metal wrapper in a plane substantially in alignment with said next
group of junctions and crevices, and again applying said
cooperative effort between said hot chemical solvent and said
transducers until the magnetite is removed from said next group of
junctions and next group of crevices; and
k. continuing in this fashion at the level of each successive group
of junctions and crevices until all of said junctions and crevices
have been cleaned.
6. In the art of maintaining a steam generator for a nuclear power
plant in which the steam generator is characterized by an enclosed
tank containing a plurality of heat exchanger tubes and a plurality
of support plates arranged transverse to and sequentially spaced
along the longitudinal axes of the tubes and forming junctions
therewith, where crevices exist between the heat exchanger tubes
and the support plates at the site of the junctions, the junctions
being thereby arranged in a series of groups, and also containing
an outer shell and a metal wrapper inside the tank which envelops
the plurality of tubes and support plates, and wherein magnetite
tends to build up within the crevices at the junctions over a
period of time, the process of removing the magnetite from the
crevices and the junctions while the heat exchanger tubes and
support plates remain in their operative positions inside the steam
generator, comprising the steps of:
a. selecting a chemical solvent which when heated to a temperature
between 120 degrees Fahrenheit and 220 degrees Fahrenheit dissolves
magnetite exposed to fresh chemicals at a rate equal to or greater
than about 1.0 inch per 24 hours;
b. adding a metal corrosion inhibitor to said chemical solvent;
c. selecting a plurality of sonic transducers wherein each sonic
transducer has a power output greater than about 0.2 watts per
square centimeter at room temperature;
d. placing said plurality of sonic transducers at a level which is
substantially in the plane of each of said groups of junctions and
in spaced locations around the circumference of and in contact with
said metal wrapper;
e. heating said chemical solvent to a temperature between 120
degrees Fahrenheit and 220 degrees Fahrenheit at a location outside
of said steam generator;
f. at least partially filling the tank with said heated chemical
solvent, so as to establish an initial level which is only a few
inches above the level of the uppermost group of junctions and
their uppermost group of crevices;
g. activating all the transducers simultaneously at each level
substantially in the plane of each group of junctions and each
group of crevices to a frequency in the range of about 2 KHZ to 200
KHZ so that sonic energy is transmitted through said chemical
solvent to each group of junctions and into and laterally of each
group of crevices whereby cavitation induced at each group of
junctions and each group of crevices cooperates with said chemical
solvent so as to enhance and accelerate the removal of the
magnetite from all of the junctions and crevices;
h. continuing the cooperative action of said hot chemical solvent
and said transducers upon each group of junctions and crevices
until the magnetite is removed from all of the junctions and all of
the crevices.
7. In the art of maintaining a steam generator for a nuclear power
plant in which the steam generator is characterized by an enclosed
tank containing a base plate on the lower portion of its interior
surface, and wherein the products of corrosion, oxidation,
sedimentation and comparable chemical reactions form a sludge pile
over a period of time on the base plate, the process of removing
the sludge pile while the base plate remains in its operative
position inside the steam generator, comprising the steps of:
a. selecting a chemical solvent which when heated to a temperature
between 120 degrees Fahrenheit and 220 degrees Fahrenheit dislodges
the sludge from the base plate within 24 hours;
b. at least partially filling the tank with said chemical solvent,
so as to establish an initial level which is only a few inches
above the level of said base plate;
c. adding a metal corrosion inhibitor to said chemical solvent;
d. selecting a plurality of sonic transducers wherein each sonic
transducer has a power output greater than about 0.2 watts per
square centimenter at room temperature;
e. placing said plurality of sonic transducers at a level which is
below the surface of said chemical solvent, substantially in the
plane of said base plate, and in spaced locations around the
circumference of the tank;
f. heating said chemical solvent to a temperature between 120
degrees Fahrenheit and 220 degrees Fahrenheit adjacent said base
plate;
g. activating said sonic transducers to a frequency in the range of
about 2 KHZ to 200 KHZ so that sonic energy is transmitted through
said chemical solvent and into said sludge pile whereby cavitation
induced at said base plate by said sonic energy cooperates with
said chemical solvent so as to enchance and accelerate the removal
of said sludge pile from said base plate;
h. continuing the cooperative actions of said hot chemical solvent
and said transducers upon said base plate for several hours until
the sludge pile is removed from said base plate; and
i. flushing said steam generator with a liquid to remove said
sludge pile from said steam generator.
8. In the art of maintaining a steam generator for a nuclear power
plant in which the steam generator is characterized by an enclosed
tank containing a base plate on the lower portion of its interior
surface, and wherein the products of corrosion, oxidation,
sedimentation and comparable chemical reactions form a sludge pile
over a period of time on the base plate, the process of removing
the sludge pile while the base plate remains in its operative
position inside the steam generator, comprising the steps of:
a. selecting a chemical solvent which when heated to a temperature
between 120 degrees Fahrenheit and 220 degrees Fahrenheit dislodges
the sludge from the base plate within 24 hours;
b. adding a metal corrosion inhibitor to said chemical solvent;
c. selecting a plurality of sonic transducers wherein each sonic
transducer has a power output greater than about 0.2 watts per
square centimenter at room temperature;
d. placing said plurality of sonic transducers at a level which is
substantially in the plane of said base plate, and in spaced
locations around the circumference of the tank;
e. heating said chemical solvent to a temperature between 120
degrees Fahrenheit and 220 degrees Fahrenheit at a location outside
of said steam generator;
f. at least partially filling the tank with said chemical solvent,
so as to establish an initial level which is only a few inches
above the level of said base plate;
g. activating said sonic transducers to frequencies in the range of
about 2 KHZ to 200 KHZ so that sonic energy is transmitted through
said chemical solvent and into said sludge pile whereby cavitation
induced at said base plate by said sonic energy cooperates with
said chemical solvent so as to enhance and accelerate the removal
of said sludge pile from said base plate;
h. continuing the cooperative actions of said hot chemical solvent
and said transducers upon said base plate for several hours until
the sludge pile is removed from said base plate; and
i. flushing said steam generator with a liquid to remove said
sludge pile from said steam generator.
9. In the art of maintaining a steam generator for a nuclear power
plant in which the steam generator is characterized by an enclosed
tank containing a plurality of heat exchanger tubes and a plurality
of support plates arranged transverse to and sequentially spaced
along the longitudinal axes of the tubes and forming junctions
therewith, where crevices exist between the heat exchanger tubes
and the support plates at the site of the junctions, the junctions
being thereby arranged in a series of groups, and also containing
an outer shell and a metal wrapper inside the tank which envelopes
the plurality of tubes and support plates, and wherein magnetite
tends to build up within the crevices at the junctions over a
period of time, the process of removing the magnetite from the
crevices and the junctions while the heat exchanger tubes and
support plates remain in their operative positions inside the steam
generator, comprising the steps of:
a. selecting a chemical solvent which when heated to a temperature
between 120 degrees Fahrenheit and 220 degrees Fahrenheit dissolves
magnetite exposed to fresh chemicals at a rate equal to or greater
than about 1.0 inch per 24 hours;
b. at least partially filling the tank with said chemical solvent,
so as to establish an initial level which is only a few inches
above the level of the uppermost group of junctions and their
uppermost group of crevices;
c. adding a metal corrosion inhibitor to said chemical solvent;
d. selecting a high boiling point fluid and placing the fluid in a
plurality of thin flexible containers, wherein the combination of
fluid and the thin flexible container has the same acoustic
impedance as said metal wrapper;
e. placing said plurality of high boiling point fluid filled
containers at a level which is below the surface of said chemical
solvent, substantially in the plane of said uppermost group of
junctions and uppermost group of crevices and in spaced locations
around the circumference of and in contact with said metal
wrapper;
f. selecting a plurality of sonic transducers wherein each sonic
transducer has a power output greater than about 0.2 watts per
square centimeter at room temperature;
g. placing said plurality of sonic transducers in alignment with
and in contact with corresponding ones of said plurality of high
boiling point fluid filled containers and also in contact with said
metal wrapper;
h. running a hot fluid through said heat exchanger tubes so that
the chemical solvent in the region adjacent said junctions and
crevices reaches a temperature between 120 degrees Fahrenheit and
220 degrees Fahrenheit;
i. activating said sonic transducers to a frequency in the range of
about 2 KHZ to 200 KHZ so that sonic energy is transmitted through
said fluid filled containers, through said metal wrapper and
through said chemical solvent, and to said junctions and into and
laterally of said crevices whereby cavitation induced at said
junctions and at said crevices by said sonic energy cooperates with
said chemical solvent so as to enhance and accelerate the removal
of the magnetite from said junctions and crevices;
j. continuing the cooperative action of said hot chemical solvent
and said transducers upon said uppermost group of junctions and
crevices until the magnetite is removed from the junctions and
crevices;
k. then lowering the level of said chemical solvent to a height
which is only a few inches above the next group of junctions and
crevices from which magnetite is to be removed, lowering said
plurality of high boiling point fluid filled containers and said
plurality of transducers to a corresponding lower location on said
metal wrapper in a plane substantially in alignment with said next
group of junctions and crevices, and again applying said
cooperative effort between said hot chemical solvent and said
transducers until the magnetite is removed from said next group of
junctions and next group of crevices; and
l. continuing in this fashion at the level of each successive group
of junctions and crevices until all of said junctions and crevices
have been cleaned.
10. The process as defined in claim 9 wherein said high boiling
point fluid is oil and said container is a thin plastic bag.
11. The process as defined in claim 9 wherein said chemical solvent
is heated to a temperature between 120 degrees Fahrenheit and 220
degrees Fahrenheit at a location outside said steam generator
before it is placed into said steam generator as described.
12. In the art of maintaining a steam generator for a nuclear power
plant in which the steam generator is characterized by an enclosed
tank containing a plurality of heat exchanger tubes and a plurality
of support plates arranged transverse to and sequentially spaced
along the longitudinal axes of the tubes and forming junctions
therewith, where crevices exist between the heat exchanger tubes
and the support plates at the site of the junctions, the junctions
being thereby arranged in a series of groups, and also containing
an outer shell and a metal wrapper inside the tank which envelops
the plurality of tubes and support plates, and wherein magnetite
tends to build up within the crevices at the junctions over a
period of time, the process of removing the magnetite from the
crevices and the junctions while the heat exchanger tubes and
support plates remain in their operative positions inside the steam
generator, comprising the steps of:
a. cutting a plurality of windows in said metal wrapper such that a
number of the windows are substantially in the plane of each group
of junctions and in spaced locations around the circumference of
and in contact with said metal wrapper;
b. selecting a plurality of sonic transducers wherein each sonic
transducer has a power output greater than about 0.2 watts per
square centimeter at room temperature;
c. placing said plurality of sonic transducers at a level which is
substantially in the plane of each group of junctions, in spaced
locations around and in contact with the circumference of said
metal wrapper, and substantially in alignment with corresponding
ones of said plurality of windows;
d. at least partially filling the tank with said chemical solvent
so as to establish a level which is only a few inches above the
level of the uppermost group of junctions;
e. adding a metal corrosion inhibitor to said chemical solvent;
f. running a hot fluid through said heat exchanger tubes so that
the chemical solvent in the region adjacent said junctions reaches
a temperature between 120 degrees Fahrenheit and 220 degrees
Fahrenheit;
g. activating all the transducers simultaneously at each level
substantially in the plane of each group of junctions and each
group of crevices to a frequency in the range of about 2 KHZ to 200
KHZ so that sonic energy is transmitted through said chemical
solvent to each group of junctions and into and laterally of each
group of crevices whereby cavitation induced at each group of
junctions and each group of crevices cooperates with said chemical
solvent so as to enhance and accelerate the removal of the
magnetite from all of the junctions and crevices;
h. continuing the cooperative action of said hot chemical solvent
and said transducers upon each group of junctions and crevices
until the magnetite is removed from all of the junctions and all of
the crevices.
13. The process as defined in claim 12 wherein said plurality of
windows are each slightly smaller than the face of said
transducers.
14. The process as defined in claim 12 wherein said plurality of
windows are each slightly larger than the face of said transducer
so that a portion of each transducer may protrude through said
wrapper.
15. The process as defined in claim 12 wherein said chemical
solvent is heated to a temperature between 120 degrees Fahrenheit
and 220 degrees Fahrenheit before it is placed into the steam
generator as described.
Description
BACKGROUND OF THE INVENTION
Large scale heat exchanger systems are essentially comprised of a
primary system which contains a large number of individual tubes
which have fluid circulating through them, and a secondary system
which consists of a second fluid surrounding said tubes contained
within a housing which enwraps both systems. In large scale heat
exchanger systems, and especially in heat exchanger systems
utilized in nuclear reactors, an often recognized problem has been
the loss of efficiency of the heat exchanger system due to the
build-up of products of corrosion, oxidation, sedimentation and
comparable chemical reations on the inner walls of the tubes
comprising the primary circulation system. More recently, it has
been discovered that the secondary system is also plagued with
similar problems such as the build-up of scale, oxides and similar
products of corrosion on the outer walls of the tubes comprising
the primary circulation system and in particular between the tubes
and the support structure for the tubes. Solutions to this problem
which are relatively non-destructive to the heat exchanger are
desired.
Ever since nuclear reactors have been employed for the generation
of electrical power, concern has been focused upon the primary heat
exchanger system and on the necessity for maintaining the tubes and
conduits of the primary circulation system therein free of anything
that could adversely affect either the heat exchanging capability
of said tubing or the unimpeded flow of fluid through said tubing.
At the same time, it was recognized that to a lesser extent, the
same concerns affected the secondary system.
In very large sized heat exchangers, and especially those used in
conjunction with steam generating nuclear reactors, the primary
system usually comprises a large number of individual tubes which
have a primary fluid circulated through them. These tubes are
placed in a large receptacle containing a secondary fluid. The
primary fluid which carries the heat is circulated through the
primary tubes in order to transfer the heat to the secondary fluid
which is circulated through the receptacle. To maximize the surface
available for heat exchange, the primary tube system contains a
very very large number of tubes which are bundled spaced apart from
each other.
Each of the large number of tubes in said primary system has a
relatively small diameter. A principal concern in such systems has
been the possibility of occluding and/or restricting the flow of
fluid through these relatively small diameter tubes. It is also
recognized that any build-up on the interior walls of the conduits
or tubes adversely affects the heat exchange properties of the
primary system.
In the past, similar concerns have not been directed to the
secondary system which, in many cases, is the steam generation
system. Therefore, in the secondary system, the principal concerns
have been only that there be an adequate supply of fluid in the
primary system, and that the opportunity and volume for the
generation of steam is made available.
The problem of maintaining the unimpeded flow of fluid through the
large number of tubes in the primary system and the efficiency of
heat exchange capability of these primary system tubes is one to
which a great deal of effort has been devoted. A chemical cleaning
process for an entire nuclear power station was described in detail
in a paper presented at the 21st Annual Water Conference of the
Engineers' Society of Western Pennsylvania on Oct. 26, 1960, by M.
F. Obrecht, et al, entitled "Chemical Cleaning of Boiling Water
Reactor and Steam Water System at the Dresden Nuclear Power
Station."
In recent years, however, a hitherto unknown but disturbing
phenomena has been encountered, especially in heat exchange systems
of some of the larger nuclear reactors. These utilize tube bundles
in the primary system which are retained in alignment by spacer
grids and support plates.
In many such systems, the tubing in the primary system was made of
a relatively corrosion resistant material such as Inconel. The
support structure for the tubing, however, was made of steel. In
the elevated temperatures and the less than ideal fluid environment
of the heat exchanger, in addition to the normal build-up of scale
and other corrosion or oxidation products on the surface of the
various components, it has been discovered that the steel support
structure, itself, oxidized to magnetite, especially in the areas
immediately adjacent the tubing in the primary system.
The support structure is comprised of spacer grids and support
plates. The steel support plates, which in many heat exchanger
designs are located in the upper portion of the tube bundles, are
fabricated with a plurality of perforations or apertures, each to
accomodate a tube of the tube bundle and to maintain the tubes
adequately spaced and aligned in the secondary chamber during the
installation process. Once the tube bundle was fastened in place,
in some heat exchanger designs there was no further need for the
troublesome support plates, but there was no easy way to remove
them.
While the creation of magnetite is not wholly unexpected, the
adverse consequences of its creation had not been fully
appreciated. Magnetite, which is a ceramic material and is
relatively "spongy", occupies a greater spatial volume than the
steel which has been oxidized to form the magnetite. As the steel
support structure oxidizes to magnetite and the magnetite builds up
at the area where the tubing is surrounded by the support plate,
the aperture between the support plate and tubing is reduced, and
magnetite eventually fills the space between the support plate and
the tubing.
As the oxidation process of steel to magnetite continues a
phenomena known as "denting" or "pinching" takes place. The tubing
in the primary system of the heat exchanger is constricted by the
increasing volume of the magnetite, and the tubing can then be
damaged and/or cracked. Further, the flow through the tubing can be
substantially impeded at the site of the restriction. Eventually,
the usefulness of the tube is reduced to virtually nothing and the
tube must be capped at its base. When over 25% of these tubes are
capped, the heat exchanger can no longer operate properly and a
major and very costly repair of the entire heat exchanger unit must
be undertaken.
The continued creation of magnetite with its volumetric increase
over the steel it has replaced also tends to cause cracking and
distortion of the steel support plates themselves. Fittings and
other restraints attached to the support plates cannot accommodate
this "expansion" process and structural stresses which are capable
of exceeding the limits of the structure are generated thereby
creating a deformation of the surrounding structure of the heat
exchanger.
Experiments have been conducted to determine ways in which the heat
exchanger system can be cleaned and the build-up removed. Chemical
methods, such as those discussed in the above-identified paper of
Obrecht, et al have been considered. Further, pilot scale
experiments have been conducted to determine the relative
efficiency of various chemical formulations in the "cleaning"
process.
It has been found that more or less conventional chemical cleaning
methods utilizing more or less accepted chemical cleaning
formulations are so slow as to endanger the integrity of the heat
exchanger system. That is, the same formulation which dissolves the
magnetite and other scale and corrosion products, if left long
enough to be effective, also attacks the basic structural elements
of the heat exchanger as well. Further, the cleaning process is
inhibited, especially in the apertures between the tubing and
support plate, if the cleaning fluid cannot be adequately
circulated or agitated to continually bring a fresh supply of
cleaning fluid to the site to be cleaned.
It has long been known that sonic cleaning is a useful method for
the decontamination of critical or precision parts and assemblies.
The American Society for the Testing of Materials published, among
other things, a special technical publication No. 342 in 1962,
entitled "Cleaning and Materials Processing for Electronics and
Space Apparatus."
In an article entitled "The Role of Cavitation in Sonic Energy
Cleaning," written for that publication by T. J. Bulat, at page
119, the phenomenon of sonic cleaning is discussed at great length.
It was suggested by Bulat, for example, that lower frequencies are
better for cleaning massive parts and for penetrating interstices.
Further, the effects of temperature were reviewed, revealing that
in water, efficiency increases with elevated temperature until
approximately 170.degree. F. Higher temperatures appear to cause a
loss in efficiency. However, it was suggested that optimum
temperature ranges are more a function of the cleaning fluid to be
utilized or the temperature at which the contaminants are most
susceptible to breakdown. As summarized by Bulat, cleaning by sonic
cavitation provides a direct and effective mechanical agitation to
speed up the soil removal process and, at the same time, maintain a
maximum concentration gradient of cleaning chemical at the surface
to be cleaned. Further, the energy for cleaning can be focused and
directed so that cavitation can be made to occur deep within the
interstices of a part or of an assembly with a complicated
geometric configuration.
Most early researchers endeavored to utilize sonic energy to keep
the interior of the primary tubes free from surface deposits during
use. See, for example, the patent to G. A. Worn, et al U.S. Pat.
No. 2,664,274. That invention was primarily directed at improving
the efficiency of heat exchangers by removing deposits from the
interior of the tubing in the primary system and preventing the
formation of deposits within said tubing during operation.
Similarly, the patent to Bernard Ostrofsky, et al, U.S. Pat. No.
3,295,596, also taught the removal of deposits from the tubes of a
heat exchanger while on-stream at elevated temperatures, through
the use of a special liquid coupling device which isolated a sonic
transducer from the adverse effects of the elevated temperatures in
the heat exchanger system.
Yet another approach utilizing sonic energy has been disclosed by
Alvin B. Kennedy, Jr., et al. U.S. Pat. No. 4,120,699 which teaches
a continuous varying of the frequency or phase relationship of
opposing accoustic wave trains which "sweep" over the surfaces of
the body to be cleaned. It would seem that the Kennedy method is
intended to clean the surfaces and restrict sedimentation. It
appears, however, that the methods and apparatus described therein
are intended for normal, preventive maintenance, and are not suited
by themselves to the problems presently being considered.
SUMMARY OF THE PRESENT INVENTION
It has been discovered, according to the present invention, that a
combination of chemical cleaning and relatively low frequency sonic
cleaning can be adapted for the removal of oxidation products, and
especially magnetite, from the structure supporting the tube bundle
in the primary system of the heat exchanger of a nuclear
reactor.
The chemical formula of magnetite is Fe.sub.3 O.sub.4. The chemical
reaction which controls the rate at which the magnetite is
dissolved is as follows:
To dissolve one magnetite molecule, 8H.sup.+ ions must be supplied,
and 2 ferric (Fe.sup.+3) ions, one ferrous (Fe.sup.2) ion, and 4
water molecules must be removed. The rate at which the reaction
proceeds is totally dependent on the available supply of hydronium
(H.sup.+ ion) and the rate of removal of iron and water. In the
small interstices between the tubes and the support plates there is
very little, if any, circulation of the chemical solution.
As a result, as the reaction proceeds and the chemicals dissolve
the magnetite in the crevices and apertures between the tubing and
support plate, the reaction rate tends to slow appreciably, as the
site of the reaction becomes saturated with the resulting products
and fresh chemicals cannot be brought to the site. It is therefore
necessary to provide a means of agitating a mixing of the chemicals
within the crevices or apertures between the tubing and support
plate causing fresh chemicals to be brought to the magnetite. The
use of sonic energy to mix and circulate the chemicals solves many
of the prior art difficulties in cleaning heat exchangers such as
steam generators.
An additional benefit to be obtained from the use of sonic energy
is that a wholly different problem which has troubled steam
generators for many years may also be attacked. There tends to be
created a buildup of sedimentation or "sludge" which accumulates in
the bottom of the heat exchanger vessel. This sludge includes
copper oxide, magnetite, and other oxidation or corrosion products
which have not adhered to the tubing or other surfaces and
therefore accumulate at the bottom. As the sludge "pile" increases
in thickness, it eventually covers portions of the tubing in the
primary system and also builds up on the support plates for said
tubing.
The presence of the sludge not only affects the rate of flow of the
fluid in the secondary system, but also degrades the heat transfer
process from the fluid in the primary system to the fluid in the
secondary system. As the sludge layer deepens, the lowermost
portion of the vessel becomes only marginally useful as a heat
exchanger.
The use of sonic energy, together with appropriate chemicals, can
first attack the sludge pile to prevent a later contamination of
the chemicals that are used in the magnetite dissolving process.
Cavitation and agitation of the sludge pile could facilitate
removal of the sludge by a flushing and/or filtration process.
Further, and according to the present invention, the use of sonic
energy to assist in cleaning and/or removal of detrimental deposits
from thermal surfaces, tends to mix thoroughly the cleaning
compounds and control the distribution of heat while preventing
local "hot spots." Further, if heat is supplied, for example, by
recirculating a heated fluid through the primary system, cavitation
is enhanced in the vicinity of the tube bundle in the primary
system. The presence of a "colder" region along the external
surface of the heat exchanger facilitates the delivery of sound
energy to the "warmer" regions surrounding said tube bundle.
As a part of the present invention, special transducers are
employed which can be placed on the outer shell of the heat
exchanger, within said shell, attached to the support plates or
created of special shapes so as to focus energy at a desired area.
Depending upon the access available, the transducers can be
provided in various locations of the interior of the heater
exchanger. If desirable, the transducer can be coupled directly to
the support plates on the interior of the heat exchanger, enabling
sonic energy to be delivered to the sites of magnetite buildup.
It is therefore an object of the present invention to provide a
process and apparatus for removing the buildup of products of
corrosion, oxidation, sedimentation and comparable chemical
reactions from various portions of heat exchanger systems such as
the location wherein the primary heat exchanger tubes in the
primary system come in contact with support plates for said tube,
and the base of said heat exchanger.
It is a further object of the present invention to provide a
process and apparatus for removing corrosion deposits such as
scale, oxides and the like from steam generators and other tube
bundle heat exchangers.
It is another object of the present invention to provide a process
and apparatus for accelerating action of chemical solvents in
removing corrosion deposits in heat exchangers.
It is a further object of the present invention to provide a
process for focusing and localizing the dissolving action of
chemical solvents in heat exchangers.
It is another object of the present invention to provide a process
and apparatus for removing magnetite from the crevices or apertures
between the tubes of the primary system and support plates for
those tubes in certain nuclear power plant steam generators and
other heat exchangers.
It is a further object of the present invention to significantly
reduce the chemical contact time required to "clean" steam
generators and other heat exchangers.
It is another object of the present invention to provide a means
for stimulating the activity of chemical solvents in the region of
steam generator or heat exchanger support plates which support
tubes within said steam generator or heat exchanger.
It is another object of the present invention to provide a process
for removing corrosion from the interstices between tubes and their
support plates in steam generators or heat exchangers without
damaging other components within said steam generator or heat
exchanger, which are chemically sensitive, such as the tubes, tube
supports, the downcomer, exterior shell, and tube sheet at the base
of the heat exchanger.
It is still another object of the present invention to provide a
means for accelerating the action of chemical solvents, by causing
agitation and local regions of high temperature and pressure at the
interfaces between the solvent and components to be cleaned.
Further novel features and other objects of the present invention
will become apparent from the following detailed description,
discussion and the appended claims taken in conjunction with the
drawings.
DRAWING SUMMARY
Referring particularly to the drawings for the purposes of
illustration only and not limitation there is illustrated:
FIG. 1, is a side sectional view of a typical heat exchanger which
contains a tube bundle through which the primary fluid is
circulated.
FIG. 2, is a side sectional view of a tube and support plate
junction which would be placed within a heat exchanger.
FIG. 3, is a side sectional view of the tube shown in FIG. 2, but
where in accordance with prior art technology part of the support
plate has been oxidized to magnetite and the magnetite has filled
the space between the tube and the support plate and further has
caused denting in the walls of the tube.
FIG. 4, is a side sectional view of a heat exchanger wherein sonic
transducers have been positioned around the circumference of the
metal wrapper which encircles the tube bundle and in alignment with
each support plate, in accordance with an embodiment of the present
invention.
FIGS. 5, 5a, and 5b are a plan view of a tube bundle and a support
plate which would be placed within a heat exchanger where as shown
in FIG. 4, sonic transducers have been placed in alignment with the
support plate and are also positioned around the metal wrapper
which encircles the tube bundle, in accordance with an embodiment
of the present invention.
FIG. 6, is a partial side sectional view of the heat exchanger
shown in FIG. 1 wherein sonic transducers have been positioned
around the circumference of the external wall of the heat
exchanger, in accordance with another embodiment of the present
invention.
FIG. 7, is a partial side sectional view of the heat exchanger
shown in FIG. 1, wherein sonic transducers have been positioned
within the heat exchanger and above the tube bundle, in accordance
with a further embodiment of the present invention.
FIG. 8, is a partial side sectional view of the heat exchanger
shown in FIG. 1, wherein sonic transducers are positioned within
the tubes of the tube bundle in accordance with another embodiment
of the present invention.
FIG. 9, is an enlarged view of a tube and its support plate with a
sonic transducer positioned within said tube, in accordance with
the embodiment of the present invention as shown in FIG. 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to the drawings of the invention in detail and more
particularly to FIG. 1, there is shown at 10 a steam generator or
heat exchanger. The external shell or envelope 12 of said heat
exchanger is a pressure vessel. Inside this external shell 12 are a
large number of tubes 14 which are the tubes that carry the primary
fluid within the primary system of said heat exchanger. Said tubes
14 pass through support plates 16 which are located along the
length of said tubes 14 and which encircle each tube 14 so as to
form a means for separating one tube from the next and allowing
each tube to remain in a fixed position within the tube bundle.
Said support plates 16 are in turn contained within a cylindrical
iron wrapper 18. The tubes 14 are typically made of a nickel alloy
such as inconel, and number on the order of 10,000, although the
configuration of the heat exchanger and corresponding number of
tubes will vary from manufacturer to manufacturer. The tubes 14
usually range from 5/8 inch to 7/8 inch in outer diameter and are
approximately 50 mils in thickness. The support plates 16, in most
current heat exchangers, are made of carbon steel and are
approximately 3/4 inch to 1 inch thick. The tubes 14 are connected
at their bottom end to an apertured plate or tube sheet 20.
In normal operation, the primary fluid 2 comes from a heat source
such as a nuclear reactor and enters said heat exchanger 10 through
a primary entrance nozzle 24. The fluid enters into the area
between the bottom of the pressure vessel external shell 12 and the
tube sheet 20. A separating wall 22 separates the inlet side 25 of
the heat exchanger 10 from the outlet side 27. The primary fluid 2
which comes from a heat source such as a nuclear reactor carries
heat with it as it is forced through the various tubes 14 and up
through the heat exchanger 10. The heat exchanger 10 illustrated in
FIG. 1 is of the U-bend type, where the tubes 14 run most of the
length of the heat exchanger 10 and are bent at the top to form a
U-shaped configuration. The U-shaped tubes 14 are attached at their
bottom to the tube sheet 20 which is mounted to the back of the
external shell 12 of the heat exchanger 10, and thereby define the
primary system of the heat exchanger 10. Upon reaching the
uppermost portion of the tubes 14, the primary fluid 2 starts back
down the opposite side of the tubes 14 and exits the heat exchanger
10 through the primary outlet nozzle 26 on the outlet side 27 of
the heat exchanger 10.
Heat which is carried by the primary fluid 2 is transferred to the
secondary fluid 4 while the primary fluid 2 is circulating through
tubes 14. Said secondary fluid 4 enters the heat exchanger 10
through secondary inlets 42 and 44 located in the external shell 12
and is located in the area surrounding said tubes 14 and within the
external shell 12. Sufficient heat is transferred to the secondary
fluid 4 so that the primary fluid 2 exiting the primary outlet
nozzle 26 is at a substantially lower temperature than it was when
it entered the heat exchanger through primary inlet nozzle 24. The
secondary fluid 4 absorbs heat carried by the primary fluid 2 and
said secondary fluid 4 becomes steam during the heat absorption
process. Said steam passes through separators 30 which remove
excess moisture from said steam, and then exits through the steam
outlet 32 at the top of the heat exchanger 10. The high pressure
steam can then be used to drive a turbine. The secondary fluid 4,
secondary inlets 42 and 44, separators 30, and steam outlet 32
define the secondary system of the heat exchanger 10.
The primary fluid 2 can be water. A gas such as helium or another
liquid such as liquid sodium can also be used for the primary
fluid. The secondary fluid 4 is usually water.
Referring to FIG. 2, said support plates 16 contain apertures or
crevices 38 through which said tubes 14 run. It is at the site of
the apertures or crevices 38 that one of the problems which the
present invention is intended to solve first occurs. In those heat
exchangers in which the support plates 16 are made of steel, the
elevated temperatures and water environment promote the oxidation
of the support plates 16 and magnetite is formed from the steel on
the exposed surfaces. As previously described, magnetite, which is
a ceramic material and is relatively "spongy", occupies a greater
spatial volume than the steel which has been oxidized to form the
magnetite. As shown in FIG. 3, as the steel support plate 16 is
oxidized to magnetite 40, and the magnetite 40 builds up at the
area where the tubing 14 is surrounded by the support plate 16, the
crevice or aperture 38 between the support plate 16 and tubing 14
is reduced, and magnetite 40 eventually fills the aperture 38
between the support plate 16 and the tubing 14. As further shown in
FIG. 3, the phenomena known as "denting" or "pinching" takes place.
The tubing 14 is constricted by the increasing volume of the
magnetite 40, and can be damaged and/or cracked. The movement of
fluid through the tubing 14 can be substantially impeded at the
site of this restriction. Although magnetite 40 will also be
created on other surfaces of support plate 16, conventional
cleaning methods, such as those described by M. F. Obrecht, et al
in his paper, Supra might be satisfactory to handle the problems at
these other areas on the support plates 16. The magnetite 40 within
the aperture 38, which causes the denting and deformation of tube
14, is not easily susceptible to the cleaning methods disclosed in
the prior art. The chemical solvents cannot easily reach into this
area. Conventional chemical cleaning methods utilizing more or less
accepted chemical cleaning formulations are so slow as to endanger
the integrity of the heat exchanger system. If these chemicals are
left long enough to be effective against the magnetite, they will
also attack the basic structural elements of the heat exchanger as
well. Conventional chemical methods known in the prior art are also
ineffective in removing the magnetite 40 at the aperture 38 because
the cleaning fluid cannot be adequately circulated or agitated to
continually bring a fresh supply of cleaning fluid to the site to
be cleaned.
The present invention involves the process of and apparatus for
removing the buildup of products of corrosion, oxidation,
sedimentation, and comparable chemical reactions from various
portions of heat exchanger systems such as the location wherein the
primary heat exchanger tubes come in contact with support plates
for those tubes. The process involves immersing the surfaces to be
cleaned in a chemical solvent capable of attacking said buildup of
products of corrosion, oxidation, sedimentation and comparable
chemical reactions at a relatively slow rate. The solvent is then
heated to desired temperatures adjacent said surfaces to be
cleaned. Finally, the process involves generating a source of sonic
energy to be used in conjunction with said chemical solvent and
directing said sonic energy through said chemical solvent and to
said surfaces to be cleaned at specific frequencies whereby
cavitation of said sonic energy is combined with said chemical
solvent so as to enhance and accelerate the removal of said buildup
of products of corrosion, oxidation, sedimentation and comparable
chemical reactions.
The present invention solves the problem of removing the magnetite
40 from the apertures or crevices 38 between said support plates 16
and said tubes 14. Referring to FIG. 4, a chemical solvent 80 is
placed inside the heat exchanger 10 and within the exterior shell
12. Sufficient chemical solvent is put into the heat exchanger to
cover said tubes 14 and said support plates 16, as shown in FIG. 4.
One chemical solvent which can be used is the combination of 8%
solution of sodium salt of ethylenediaminetetracetic acid (EDTA),
plus 4% solution of citric acid plus an effective amount of a
standard corrosion inhibitor (such as 0.6% of OSI-1 corrosion
inhibitor sold by Halliburton Services).
Said chemical solvent 80 can be heated to a desired temperature,
which is between 120.degree. F. and 220.degree. F. A preferred
heating method would be the utilization of the primary circulating
system to circulate a heated fluid through the tubes 14 until the
solvent has reached its desired temperature. Once achieved, that
temperature can be maintained by adding heat through the primary
system. Alternatively, the chemical solvent 80 can be heated
externally and then the heated solvent 80 can be added to the
secondary system inside the heat exchanger 10. This method is less
desirable than the preferred method because it requires the heating
and circulating of a potentially hazardous and corrosive substance.
Further, utilizing a benign heating fluid through the tubes 14 in
the primary system provides the additional benefit of inducing a
convection flow of the chemical solvent 80 at the interfaces of the
tubes 14 and the support plates 16. Care should be taken that the
temperatures at the interfaces of the tubes 14 and the support
plates 16 during the cleaning process does not exceed the desired
levels since undue heating adversely affects the efficiency of the
sonic cleaning process.
Sonic energy is generated from transducers 50 which contain a face
51 and a rear portion 53. Referring to FIGS. 4 and 5, the preferred
placement of the sonic transducers 50 is shown in the form of a
ring 52 of such transducers encircling the wrapper 18 which in turn
encircles the support plates 16 and tubes 14. The wrapper 18
significantly reduces the effectiveness of sonic energy generated
by the sonic transducers 50. Further, a problem is created because
the thin fluid layer of chemical solvent 80 which is trapped
between the transducer face 51 and the wrapper 18 cavitates or
boils due to the heat generated by the transducer 50 and this is
turn decouples the transducer 50 from the wrapper 18. This problem
is solved by either of the following means. The first and preferred
method shown in FIG. 5b, involves placing a thin layer of high
boiling point fluid 90 between the transducer face 51 and the
wrapper 18. The fluid 90, such as oil, can be placed in a container
92 such as a flexible plastic bag which is approximately 1/8 inch
thick, and will remain in place by pressure between the face of the
transducer 50 and the wrapper 18. The combination of this coupling
fluid 90 and the container 92 for the fluid 90 should have the same
acoustic impedance as the metal wrapper 18 in order to have good
sonic transmission. The transducers 50 are held firmly against the
fluid filled container 92 or metal wrapper 18 by mechanical means
such as a support wedge 99 placed between the rear portion of the
transducer 53 and the internal vertical portion of the shell 12, or
by direct mechanical or magnetic attachment to the metal wrapper
18. In the second method, shown in FIG. 5a, windows 94 whose
dimensions are approximately the size of the transducer face 50 are
cut in the wrapper 18 portion in front of each transducer 50. After
the cleaning process has been completed, these windows 94 are
sealed by replacing the metal removed on cutting the window 94 in
the wrapper 18 and welding the piece of metal back in place. When
the windows 94 are cut slightly smaller than the face of the
transducer 51, the transducer can be held in place against the
metal wrapper 18 by direct mechanical or magnetic attachment to the
metal wrapper 18, or by mechanical means such as a support wedge 99
placed between the rear portion of the transducer 53 and the
internal vertical portion of the shell 12. When the window 94 is
cut slightly larger than the face of the transducer 51, part of the
transducer 50 can be placed through the metal wrapper and will
remain in place in this fashion.
The ring 52 of transducers 50 is energized to radiate sonic energy
in the frequency spectrum between 2 KHZ and 200 KHZ. The choice of
these frequencies permits improved coupling of the sonic energy
into the chemical solvent 80 and to the sites of interest such as
the aperture 38 between the support plates 16 and tubes 14. The
optimum cleaning interval for any heat exchanger can be
experimentally determined, but it is believed that approximately 24
hours of sonic irradiation should be adequate to clean the first or
uppermost plate.
Sonic irradiation can be extended for longer periods as necessary.
Results of experimental tests have shown that over a 24 hour
cleaning period negligible adverse effects from the chemical
solvent 80 are experienced by the other components. Some
experiments suggest that the cleaning process may be accomplished
in somewhat less time and, in any given heat exchanger, it may be
possible to visually observe the progress of the cleaning, at least
insofar as the uppermost support plate is concerned, since it might
be subject to visual monitoring.
As each plate 16 is cleaned, the fluid level is dropped as is the
ring 52 of transducers 50 and the process is repeated. This
procedure, has, however, the effect of exposing at least the lower
portions of the vessel to the chemical solvent for longer periods
of time. In view of the longer, but "passive" exposure to the
solvent, as one proceeds toward the bottom of the tank the period
of time during which the sonic transducers are operated at each
fluid level is progressively reduced.
It has been experimentally determined that using the chemical
solvent 80 alone without sonic energy irradiation would require
approximately 8 days to achieve a similar cleaning effect as is
achieved by the present invention in only one day. Therefore, the
adverse affects of the solvent 80 on the components of the heat
exchanger are substantially reduced due to the significant decrease
in time that the solvent 80 must remain inside the heat
exchanger.
The embodiment of the present invention described above requires
the use of a ring of sonic transducers around the outer
circumference of the metal wrapper 18 of the heat exchanger 10. As
each support plate and tube is cleaned, the cleaning solvent level
80 is lowered to a few inches above the next support plate and the
ring 52 of sonic transducers 50 is lowered to be in alignment with
the next support plate to be cleaned, as shown in FIG. 5. A key
point in this process is that the level of chemical solvent must be
only a few inches above the surface area to be cleaned. If the
level is much higher, the effectiveness of the sonic energy in
creating the cavitation at the site to be cleaned is significantly
reduced.
In order to create cavitation at the site to be cleaned, the
transducers must be able to generate a power output greater than
about 0.2 watts per square centimeter at room temperature. This
power density limitation on the transducers is demonstrated in the
textbook "Sonics--Techniques For The Use Of Sound And Ultrasound In
Engineering And Science, by Theodor F. Huetter and Richard H. Bolt,
Fourth Edition published in 1965," pages 228 to 232. Referring
specifically to FIG. 6.13 on page 230 of said textbook, in order to
produce cavitation in degassed water at room temperature, the
transducer must generate approximately 0.2 watts per cubic
centimeter. As shown by the chart, if the transducer has a power
output greater than about 0.2 watts per square centimeter,
cavitation will be produced over a broad frequency range.
An alternative embodiment of the present invention is shown in FIG.
6 wherein the ring 52" of transducers 50" is wholly exterior to the
heat exchanger 10 and is placed around the outer circumference of
the external shell 12 of the heat exchanger 10. In this embodiment,
the actual cleaning procedure would be substantially similar to
that of the preferred embodiment described above except that the
ring 52" of transducers 50" is mounted on the outside and must be
"coupled" to the interior of the vessel. The heat exchanger 10 is
filled with the chemical solvent 80 which is heated to the desired
temperature. The ring 52" of transducers 50" is placed at the
height of the uppermost support plate 16 and is energized. The
sonic energy is transmitted to the interior through a sonic coupler
58 which may include a fluid held in place by seals 60. As each
support plate and tube is cleaned, the cleaning solvent level 80 is
lowered to just above the next support plate and the ring 52" of
sonic transducers 50" is lowered to be in alignment with the next
support plate to be cleaned. The patent to Ostrofsky, U.S. Pat. No.
3,295,596 illustrates a particular coupler apparatus which would be
employed. The embodiment of the present invention is designed to be
used with those heat exchangers where interior access is either
severely limited or is considered too hazardous.
The rings 52, 52" of transducers 50, 50" can be successively
repositioned in the vertical direction during the cleaning process.
At each repositioning, the fluid level is lowered to a height above
the transducer ring sufficient to support and maintain the
efficient transmission of sonic radiation to the surfaces to be
cleaned. As shown, the tubes and plates are cleaned in
increments.
It may be sufficient that each increment includes one of the
support plates and that a suitable interval of time is employed to
irradiate the plate. The time required for each of the plates can,
of course, be experimentally determined. However, it is believed
that although the sonic energy is primarily directed at a
particular plate and its tube intersections, the adjacent plates
will also benefit from the sonic energy and the cleaning of those
plates will proceed, as well.
The time required for the later increments may be progressively
less, so that by the time the lowermost plate is reached, the
required cleaning time for this plate will be substantially less
than for the others. The total time during which the lowermost
portions of the heat exchanger have been immersed in the solvent
bath will, nevertheless, be substantially less than required
through the use of solvents alone.
Because the cleaning action of the solvent 80 is intensified, it is
possible to use a chemical solvent at greater concentrations for
shorter cleaning time. Depending upon the construction of the heat
exchanger and the materials used in its fabrication, some optimum
combination of solvent strength and cleaning time can be devised to
minimize the unwanted effects of the solvents on the structural
components.
Many of the special fluid properties necessary to maximize the
efficiency of the sonic cleaning process, can be achieved in the
compounding of the chemical solvent. The solvent should be active
at relatively low temperatures (below 200.degree. F.) and be
substantially immune to the effects of sonic cavitation. Further,
the solvent should optimize those properties which support high
cavitation energy levels such as high surface tension, low vapor
pressure and low viscosity.
The utilization of sonic energy in the cleaning process not only
has a direct effect on the scale, corrosion products and magnetite,
but also enhances the effect of the chemical solvent by agitating
and circulating the solvent in the regions being cleaned. This
agitation tends to carry away "saturated solvent" and waste
products, and brings fresh solvent to the region so that the
solvent does not lose its effectiveness.
While the process of cleaning the particular surfaces of the heat
exchanger has been described, the presence of the sludge pile, and
its effect on the cleaning process has not been considered
heretofore. Because the sludge pile does contain a large quantity
of loose sediment, magnetite, copper and other corrosion products,
the fluid agitation caused by the sonic cavitation may stir up the
sludge and its presence may actually interfere with the cleaning
action of the solvent upon the structural parts.
It may therefore be desirable to initiate a preliminary cleaning
process in an attempt to remove the sludge pile before any other
cleaning is attempted. For this operation, it may be preferable to
have transducers mounted to the exterior shell 12 of the heat
exchanger 10 and to use a fairly concentrated and relatively strong
chemical solvent which just covers the sludge pile only and is not
brought in contact with the remaining structural elements. Is is
also possible that through the application of sonic energy alone,
the sludge pile can be "stirred up" sufficiently to enable a
flushing operation to carry away a substantial portion of the
sludge pile, without the need for chemical solvent action.
If the removal of the sludge pile is not to be undertaken, it may
be necessary to provide some physical isolation of the sludge pile
from the cleaning solvent so as not to contaminate and/or
neutralize the chemical solvent before it has had a change to work
on the structures to be cleaned. In this event, it may be necessary
to provide a blanketing layer of an appropriate liquid which will
effectively isolate the sludge pile from the chemical solvent
bath.
Another alternative embodiment of the present invention is shown in
FIG. 7 wherein the ring 52' of transducers 50' are placed inside
the heat exchanger 10 and inside the metal wrapper 18, and over the
bundle of and substantially parallel to the tubes 14. The
effectiveness of this placement may be limited if the vessel is
quite deep. Very deep vessels might not be optimally served.
However, for those heat exchangers in which the embodiment can be
successfully employed, it offers the advantages of both easier
installation and removal.
Turning next to FIG. 8 and FIG. 9, there is shown an additional
alternative embodiment of the present invention. As shown,
individual sonic transducers 70 are placed within selected tubes 14
of the primary system. Energizing these transducers 70 can
concentrate the sonic energy in the immediate vicinity of the tubes
14. By appropriate positioning of a transducer 70, along the axis
of the tube, the energy can be successively directed to the
deposits at each of the support plates 16, in turn. This
application of the present invention can also be used to clean
tubes which are badly corroded internally or which are dented. The
cleaning of these tubes would prevent further tube damage and would
eliminate the need to remove tubes from service by plugging them at
the tube sheet 20.
Access to the interior of the tubes can be achieved either from the
manifold area at the primary inlet 24 and primary outlet 26, or,
selected tubes can be cut and later repaired when the cleaning
process has been concluded. These transducers 70 mounted interior
to the tubes 14 could be employed in conjunction with other
transducers which could be either mounted on the exterior wall 12
of the heat exchanger 10 or mounted on the metal wrapper 18 to
operate in a cooperating and coordinated fashion. Alternatively, if
relatively unrestricted access can be gained to the interior of the
heat exchanger, some transducer elements can be attached directly
to support plates 16.
As shown in FIG. 8, it is also possible to utilize pressure
sensitive transducers 72 at various locations within the vessel to
determine the magnitude of sonic energy at selected locations. This
monitoring capability can increase the efficiency of the cleaning
process since the sonic transducers 70 can then be selectively or
differentially driven to maximize the cleaning action at desired
locations.
Other variations and modifications will appear to those skilled in
the art in terms of instrumentation, directing the sonic energy and
using measurements of water pressure and frequency to determine the
energy level at any given point within the heat exchanger system.
Where time is a critical factor, as in the cleaning of the heat
exchanger portion of a nuclear reactor, the present invention
provides time savings that are appreciable and significant.
Of course, the present invention is not intended to be restricted
to any particular form or arrangement, or any specific embodiment
disclosed herein, or any specific use, since the same may be
modified in various particulars or relations without departing from
the spirit or scope of the claimed invention hereinabove shown and
described of which the methods shown are intended only for
illustration and for disclosure of an operative embodiment and not
to show all of the various forms of modification in which the
invention might be embodied.
The invention has been described in considerable detail in order to
comply with the patent laws by providing a full public disclosure
of at least one of its forms. However, such detailed description is
not intended in any way to limit the broad features or principles
of the invention, or the scope of patent monopoly to be
granted.
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